Field of the Invention
This invention relates to groundwater recovery systems, and more particularly to methods and systems for controlling and automating groundwater recovery.
Controlling groundwater contamination is a problem facing many communities today. When contaminants from a pollutant source contacts a groundwater aquifer, a groundwater contaminant plume is formed. This contaminant plume may migrate in the direction of the groundwater flow. In order to provide remediation of the groundwater aquifer and control migration of the contaminant plume, many environmental remediation programs today use a pump-and-treat operation. The cost of such an operation, however, can be quite high. In many cases, the pump-and-treat operation extends over many years thereby incurring--in addition to the initial construction costs--annual costs to maintain the system and pump and decontaminate the groundwater.
In a pump-and-treat operation, the migration of the contaminant plume is controlled by establishing a hydraulic barrier. This is accomplished by boring a well which penetrates into the groundwater aquifer and removing the contaminated groundwater for decontamination. To monitor the effectiveness of the remediation, contaminant concentrations are tested at monitoring wells and the results reported to regulatory agencies. These tests, however, can only determine if the contaminant concentrations are properly controlled at those sites at the time of the test. To comply with regulatory requirements, pump-and-treat sites may be required to monitor contaminant concentrations and/or water levels. In the vast majority of cases, this information is only utilized in a report showing groundwater levels, and on rare occasions, the capture zones, which is submitted to the required regulatory agencies.
Under the prevailing design approach to pump-and-treat programs, the establishment of a constant flow rate is of paramount importance. This flow rate is site specific and is calculated to capture the contaminant plume within a predetermined capture zone. Although a flow meter may be used in the groundwater extraction well to track the pumped water, transducers located in the groundwater extraction well, for instance, are not used since any information obtained from that location would be unreliable with respect to determining both groundwater levels, capture zones, and/or contaminant concentrations.
An aquifer, being a dynamic hydraulic system, is impacted by many variables such as changes in the saturated thickness, weather, impoundments and the presence of rivers and streams. Changes to these variables can lead to greatly changed pumping conditions--and thus the constant flow rate initially calculated may no longer be suitable. For instance, an increase in the groundwater level may lead to an under-pumping situation where using the predetermined constant pumping rate is insufficient to maintain the desired predetermined capture zone. This results in inadequate contaminant cleanup and compliance violations. Conversely, a drop in the groundwater level may lead to an over-pumping situation where using the predetermined constant pumping rate results in pumping out, treating and remediating more groundwater than necessary, thereby increasing operating costs.
These problems are evident at current sites using pump-and-treat systems. For instance, it is believed that only a handful out of approximately 2,000 federal sites using pump-and-treat systems have been successful; and that another 10,000 private sites are using this technique with varying degrees of success. These systems apparently do not work well, in part, due to over-pumping and/or under-pumping of the contaminated groundwater.
Although pumping rates may be adjusted in the early stages of treatment, pumping rates are not conventionally adjusted based on information obtained for regulatory compliance. If the information is used to adjust the pumping rate, it is conventionally obtained only long after conditions have changed and from locations away from the capture zone boundary. In addition, any changes based upon this information are manually implemented. As can be seen, the foregoing is a difficult and time consuming process, and fails to provide any means whereby a more dynamic response to changing conditions may be effectuated.
There is accordingly a need for a groundwater recovery system which provides a high degree of hydraulic control over the removal of the contaminant plume, is cost-effective, and more importantly, raises the confidence level that the pump-and-treat remediation operation is effective and in compliance with environmental regulations.